Field of Endeavor
The present application relates to processing and more particularly to Laser-Driven Hydrothermal Processing.
State of Technology
Removal of the surface of materials such as concrete, brick, and rock/minerals can be accomplished via grinding or intense abrasive water jets or electric-discharge shock chipping and flaking of concrete. Laser scabbling, which uses a 5 kW laser to heat concrete in air to its boiling/flaking/cracking point has been demonstrated. None of these processes employs transient dissolution of the surface as its primary mechanism and none offers gentle, μm-scale control of the material removal.
“Laser peening” uses intense laser pulses also directed at metal targets that are submerged in water, in order to generate a plasma and counter-propagating shock waves at the interface between the metal target and the water. The interaction between laser pulses and a metal target, whether submerged or not, is fundamentally different than the interaction between laser pulses and a dielectric target, such as concrete, brick, or rocks. Conductors, such as metals, possess vastly higher electrical conductivity than do dielectrics, and the laser light striking a metal target is absorbed entirely within a skin depth that is at most a few μm. Except in cases of extremely high-power laser pulses, whose use would be inappropriate for an energy-efficient, gentle, and controlled process, dielectric materials absorb light over a much longer penetration depth. Because metals absorb the laser pulses so strongly, it is not surprising that it is relatively easy to generate high temperatures and pressures at the interface between a submerged metal and the submerging fluid.
Hydrothermal processing is a technique to grow purified crystals of materials including quartz [SiO2] and emerald [Be3(Al,Cr)2Si6O18]. Information about hydrothermal processing is provided in the article: “Pulsation processes at hydrothermal crystal growth (beryl as example),” Journal of Crystal Growth 206, 203-214 (1999) by V. G. Thomas, S. P. Demin, D. A. Foursenko, and T. B. Bekker and the article “Hydrothermal growth of α-quartz using high-purity α-cristobalite as feed material,” Materials Research Bulletin 28, 1201-1208 (1993) by M. Hosaka and T. Miyata. Average growth temperature for beryl was −600° C. and pressure was 1.5 kbar for pure water at given temperatures. The duration of runs was 15 to 25 days, growth rate was 0.1 mm/day. For quartz, the growth was carried out for 5-22 days. Quartz growth rates, in growth with high degree fillings exceeding 75%, were approximately 0.2-0.6 mm/day in the Z direction and approximately 0.1-0.2 mm/day in the X direction. Traditional hydrothermal processing requires containment vessels that can withstand sustained high temperatures and pressures and the process is very slow. Thus, traditional hydrothermal processes would have no practical application to treating large surfaces of buildings, etc.